U.S. Pat. No. 4,513,006, which is hereby incorporated by reference, discloses a class of novel anti-epileptic compounds. One of these compounds, 2,3,4,5-bis-O-(1-methylethylidene)-β-D-fructopyranose sulfamate, known as topiramate, has been demonstrated in clinical trials of human epilepsy to be effective as adjunctive therapy or as monotherapy in treating simple and complex partial seizure and secondarily generalized seizures (E. Faught, B. J. Wilder, R. E. Ramsey, R. A. Reife, L. D. Kramer, G. Pledger, R. M. Karim, et al., Epilepsia, 36 (S4) 33, (1995); S. K. Sachdeo, R. C. Sachdeo, R. A. Reife, P. Lim and G. Pledger, Epilepsia, 36 (S4) 33, (1995)). U.S. Pat. No. 4,513,006 , No. 5,242,942, and No. 5,384,327, which are hereby incorporated by reference, disclose processes for the preparation of these novel anti-epileptic compounds.
Topiramate is currently marketed for the treatment of simple and complex partial seizure epilepsy with or without secondary generalized seizures in Great Britain, Finland, the United States and Sweden and applications for regulatory approval are presently pending in numerous countries throughout the world.
Ehrenberg et al in U.S. Pat. No. 5,998,380 disclose pharmaceutically acceptable derivatives of the following formula (A)

wherein the substituents are a described in U.S. Pat. No. 5,998,380. By pharmaceutically acceptable derivative is meant any pharmaceutically acceptable ester or salt of such ester of the compounds of the formula (A) or any other compounds which upon administration to the recipient is capable of providing (directly or indirectly) a compound of the formula (A) or an anti-migraine active metabolite or residue thereof.
Pharmaceutically acceptable salts of the compounds of the formula (A) include those derived from pharmaceutically acceptable, inorganic and organic acids and bases. Examples of suitable acids include hydrochloric, hydrobromic, sulfuric, nitric, perchloric, fumaric, maleic, phosphoric, glycollic, lactic, salicylic, succinic, toluene-p-sulphonic, tartaric, acetic, citric, formic, benzoic, malonic, naphthalene-2-sulphonic and benzenesulphonic acids. Other acids such as oxalic acid, while not in themselves pharmaceutically acceptable, may be useful in the preparation of salts useful as intermediates in obtaining compounds useful in the method of the patent and their pharmaceutically acceptable acid addition salts.
Salts derived from appropriate bases include alkali metal (e.g. sodium), alkaline earth metal (e.g. magnesium) ammonium and NR4 (where R is C1-4alkyl) salts.
McElroy, S. L. in PCT application WO 00/50020 disclose pharmaceutically acceptable salts of compounds of the following formula (B)

wherein the substituents are as described in PCT application WO 00/50020. Pharmaceutically acceptable salts of the compounds of the formula (B) include, for example, alkali metal salts, such as sodium and potassium; ammonium salts, monoalkylammmonium salts; dialkylammonium salts; trialkylammonium salts; tetraalkylammonium salts; and tromethamine salts. Hydrates and other solvates of the compound of the formula (B) are also included within the scope of compounds.
Pharmaceutically acceptable salts of the compounds of formula (B) can be prepared by reacting the compound of the formula (B) with an appropriate base and recovering the salt.
Dewey et al, in PCT application WO 00/07583 disclose pharmaceutically acceptable salts of topiramate. As defined in the specification, pharmaceutically acceptable salts include those salt-forming acids and bases which do not substantially increase the toxicity of the compound. Some examples of suitable salts include salts of mineral acids such as hydrochloric, hydroiodic, hydrobromic, phosphoric, metaphosphoric, nitric and sulfuric acids, as well as salts of organic acids such as tartaric, acetic, citric, malic, benzoic, glycollic, gluconic, gulonic, succinic, arylsulfonic, eg. p-toluenesulfonic acids, and the like.
We now describe novel salt forms of anticonvulsant derivatives, including novel salt forms of topiramate, which forms are suitable for use in the preparation of pharmaceutical formulations.